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So I've had my 2021 C8 for a year now. Something that happens on occasion, since new, is that on the 1-2 shift I will get a very loud pop from the exhaust immediately followed by a split second bogging of the engine. I can't replicate it or know when it will happen. I drive in Z mode and manual shift 100% of the time. In normal driving I shift at 1200-1500 rpm under light throttle. It's never happened when driving fun or at higher rpm shifting. The pop that is made is significantly louder than the normal pips the exhaust makes
I'm thinking the backfire caused by the unburned fuel is causing the bog to occur but not sure it it's causing damage. I have no codes popping up and the car was just in last month for its first oil change. Car otherwise drives flawlessly.
I've driven manuals exclusively for years (this is my first DCT/Auto) and I never upshift below 2,000 - 2500 rpm. As Fast Dawg said above, it might be the computer trying to compensate for a lugging engine.
Try shifting at a little higher RPM even at low throttle and see if it goes away.
I absolutely love the pop but have never experienced any bogging. In fact i sometimes put the car in manual mode, gas the engine up to some higher revs and then let off on the gas to create some back pressure and then shift into second gear just to get some serious pops. Lol
So I've had my 2021 C8 for a year now. Something that happens on occasion, since new, is that on the 1-2 shift I will get a very loud pop from the exhaust immediately followed by a split second bogging of the engine. I can't replicate it or know when it will happen. I drive in Z mode and manual shift 100% of the time. In normal driving I shift at 1200-1500 rpm under light throttle. It's never happened when driving fun or at higher rpm shifting. The pop that is made is significantly louder than the normal pips the exhaust makes
I'm thinking the backfire caused by the unburned fuel is causing the bog to occur but not sure it it's causing damage. I have no codes popping up and the car was just in last month for its first oil change. Car otherwise drives flawlessly.
I have the pops and I like them. I never get a lag.
But I remain uncertain about the cause of the pop - is it really unburned fuel entering the exhaust system and being ignited after entering the exhaust system - or is just ignited fuel that is still burning or expanding when the exhaust valve opens (caused by the way that the ECM modulates the engine power during shifts). Two reasons I question the unburned fuel theory: 1) the pops will happen while the car is till cold, so is the exhaust system really hot enough to ignite unburned fuel, and 2) isnt unburned fuel entering the exhaust system a key cause of catalytic converter damage/failure?
I have the pops and I like them. I never get a lag.
But I remain uncertain about the cause of the pop - is it really unburned fuel entering the exhaust system and being ignited after entering the exhaust system - or is just ignited fuel that is still burning or expanding when the exhaust valve opens (caused by the way that the ECM modulates the engine power during shifts). Two reasons I question the unburned fuel theory: 1) the pops will happen while the car is till cold, so is the exhaust system really hot enough to ignite unburned fuel, and 2) isnt unburned fuel entering the exhaust system a key cause of catalytic converter damage/failure?
I suspect it is unburned fuel entering the exhaust and then ignited.
When I was a kid we thought it was fun to turn off the ignition while coasting to fill up the exhaust system with an air/fuel mixture and then turn the ignition back on while we passed a pedestrian. Sounded like a shotgun blast. It was hilarious until we blew off and ran over the muffler on my mom's car and had to pick it back up from the street.
Sorry, everyone, when I posted I messed up. I shift at 2200-2500rpm for regular driving. It's then when I get the occasional bog. And the pop that happens is not the normal pop. It's very loud, like a backfire, and not the regular pops the car typically makes
I suspect it is unburned fuel entering the exhaust and then ignited.
When I was a kid we thought it was fun to turn off the ignition while coasting to fill up the exhaust system with an air/fuel mixture and then turn the ignition back on while we passed a pedestrian. Sounded like a shotgun blast. It was hilarious until we blew off and ran over the muffler on my mom's car and had to pick it back up from the street.
I did the same thing with my parents 1967 VW. In that case, for sure it was unburned collecting. But it did not ignite until I turned the ignition back on. What ignited it (since it did not ignite until the ignition was back on)? I guess hot gas coming from the exhaust, I suppose.
Sorry, everyone, when I posted I messed up. I shift at 2200-2500rpm for regular driving. It's then when I get the occasional bog. And the pop that happens is not the normal pop. It's very loud, like a backfire, and not the regular pops the car typically makes
I get both kinds of pop. Some are like pop. Others crack, like a backfire. In my case the cracks happen with harder acceleration. But still, no lag.
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Hope you can figure this out, epecially the bogging of the engine. As Zymurgy suggested, try driving in something other than Z mode and see if it still happens.
Try running in Z-Mode but do NOT put the DCT into manual mode. Let it do its own thing and see if that eliminates the bogging.
Like I said, hard to replicate and typically only happens like once a month. It's my daily driver so driving it in auto mode would take away from the pleasure and given how infrequent it is, it would be a long time before i could say if auto mode fixes the issue. Was just trying to see if anyone else noticed the same issue
Sorry, everyone, when I posted I messed up. I shift at 2200-2500rpm for regular driving. It's then when I get the occasional bog. And the pop that happens is not the normal pop. It's very loud, like a backfire, and not the regular pops the car typically makes
Ok, that sounds better. So less likely to be issue with lugging the engine.
Have you tried just driving in D(auto)? (Z mode or otherwise) does it still bog?
I am starting to wonder if you have a misfire problem related to a plug/coil. If this is occuring around the time the timing is retarded during those normal "pops" on shifting between 1,2 and 3rd gears then perhaps this is leading to some unburnt fuel igniting in the header/s?
Do you have an OBD2 scanner? I have seen misfire problems reported by my scanner where there is NO CEL, and NO CODES.
Ok, that sounds better. So less likely to be issue with lugging the engine.
Have you tried just driving in D(auto)? (Z mode or otherwise) does it still bog?
I am starting to wonder if you have a misfire problem related to a plug/coil. If this is occuring around the time the timing is retarded during those normal "pops" on shifting between 1,2 and 3rd gears then perhaps this is leading to some unburnt fuel igniting in the header/s?
Do you have an OBD2 scanner? I have seen misfire problems reported by my scanner where there is NO CEL, and NO CODES.
It's on my list to pick up a scanner this weekend so I'll see if anything comes up. Thanks
Sorry, everyone, when I posted I messed up. I shift at 2200-2500rpm for regular driving. It's then when I get the occasional bog. And the pop that happens is not the normal pop. It's very loud, like a backfire, and not the regular pops the car typically makes
OK. That does sound strange and I shift in the same range when I'm using the paddles. I'm in sport mode but that shouldn't make a difference as far as the bogging sensation you are feeling. Sorry you are experiencing this because like you said - it's going to be hard to replicate for a dealer. I would get a code reader as @dohabandit suggests to see what it tells you. Good luck and let us know what you find. I know you have my curiosity peaked with the corrected information you provided about your RPMs while shifting.
Popping causes bogging
